Electric switch



Aug. 9, 1960 T. A. FJELLSTEDT ETAL 2,948,794

ELECTRIC SWITCH Filed March l, 1957 3 Sheets-Sheet 1 INVENTORS, Thorstenf?. E/ZZstedt q /Qaert Enes (/ter' Kanaals/fn dames Sedia/ast Aug 9,1960 T. A. FJELLSTEDT r-:T AL 2,948,794

ELECTRIC SWITCH 3 Sheets-Sheet 2 Filed March 1, 1957 INVENTORS. Thorstena? F'cZZstedt Robert E'Jne.: falter Kaa/aZs/fg, Jmes JT Seagmst ttar'mgyAug. 9, 1960 Filed March l, 1957 T. A. FJELLSTEDT ET AL 2,948,794

ELECTRIC SWITCH y s sheets-sheet :s

' Patented Aug. `9,1960

ELECTRIC SWITCH Filed Mar'. l, 1957, Ser. No. 643,429

7 Claims. (Cl. 200--166) 'This invention pertains generally to electricswitches and more particularly to improved means for transferringcurrent through the joints between relatively movable parts thereof.

The invention is illustrated as an improvement over two general types ofprior art air disconnect switches. The rst of these has an elongatedblade that is adapted to turn on its longitudinal axis and swing on atransverse axis into and out of direct engagementV with a pair ofexposed stationary contact jaws located at opposite sides of thetransverse axis. In such a switch, the blade ordinarily has a crosssection whose dimensions are unequal so that the blade enters betweenboth sets of jaws on its lesser dimension and is then rotated into highpressure engagement on its greater dimension, thus tending to spread thejaws. Obviously, maximum operating eort must be exerted when the highpressure engagement is being made or broken simultaneously at both endsof the blade. The arrangement suiers the disadvantages of having highspots which must be overcome at the most critical period during switchoperation and it further lends itself to impairment by ice and corrosionsince the blade and cooperating Contact jaw in the region of the bladehinge must necessarily be exposed to the atmosphere.

A second type of prior art switch improved by the present invention isone wherein an attempt is made to carry current through or past thejoints interconnecting the switch parts. Examples of this type areflexible shunts, cam type wiping contact ngers that bridge the jointsand rotatable screw connections.

Most of the aforementioned switch designs are inherently limited insofaras the possible number of current interchange points attainable in ajoint is concerned for although they may seek to establish line or areacontact between parts they in fact develop only one or two points ofcontact between high spots on adjacent conductive parts. Generally theproblem of attaining more points of interchange is impossible toovercome in those designs because of space limitations and there resultsa switch that requires excessive operating'eifort and that undergoes anear maximum permissible thermal rise during use.

An important object of the instant invention is to eliminate the needfor an exposed contact jaw at the hinge end of a disconnect switch bladeby substituting therefor a novel multiple path concealed cuurentinterchange contact in the joints between movable switch parts. By thismeans the mechanical losses that occur at the most critical time, thatis, when the blade is entering or leaving its cooperating jaw, arereduced. This concentrates all available operating effort on the bladefor breaking ice and corrosion if any are present. Likewise, it permitssimplication of the `switch construction at the hinge end of the bladeIand obviates the obstacle of trying to tit larger contact jaws and morehigh pressure current interchange points into this region of limitedspace when designing for greater current carrying capacity.

A more specic object is to provide a current transfer means thatproduces the electrical ettect of high contact pressure through amultiplicity of lower pressure contact points which subdivide the ow ofcurrent into paths that are distributed over a great area in order toaugment thermal dissipation, to obviate electromagnetic effects, and toreduce friction incident -to prior art high pressure contacts.

Another'object to provide a current interchange contact that is simplein form, economical to manufacture in all its aspects and that iscompact, so that it may be easily installed without exceedingdimensional requirements of good switch design. j

A further object is the provision of a multiple point currentinterchange contact which in a single element combines the functions ofcurrent carrying and developing contact pressure and which is notinherently limitedin the number of interchange points but whose currentcarrying capacity may be multiplied by the simple expedient of stackingthe novel contacts in parallel or by merely increasing the diameter ofone of them.

Another object is to provide an interchange contact that is easy toincorporate in a bearing assembly and lends itself to being permanentlylubricated, sealed and protected against corrosion to the end thatcontact pressure may be established during assembly which will be un-Vaiected by wear, ice accumulation or deleterious atmospheric conditions.

Another object is' to provide a current interchange contact thatmaintains circuit continuity at the same eiiiciency while the switchpart-s are undergoing movement as under static conditions when theswitch' is closed. Fulfillment of this object is particularly importantWhere the switch is adapted to open under vload in conjunction with aload interrupter.l

Other more specific objects will 'be perceptible wheny proceedingthrough the ensuing description of the in vention. Y

In accordance with a preferred embodiment of the invention exempliiiedin an air disconnect switch,'the novel current interchange contactcomprises a multiple convolution helical spring member attached at itsendsA` to form a toroidal shape. The toroidal shaped contact may beconined in the joint between concentric members, such as tubular bladeand cylindrical housing, or between adjacent, relatively rotatablenominally planar members, the latter hereinafter being called a parallelplate application. In the preferred embodiments, one of the members isprovided with a V-groove that contains and positions the spring-likecontact by bearing in tangency against each convolution at two pointsand the other member may be smooth and bearing in tangency to a pointsubstantially opposite, so that two parallelv current paths are createdin each convolution. Where'A the members are concentric, the springcontact has all of its convolutions tilted in their naturalcircumferential ldirection around its toroidal shape. Where the membersare nominally parallel `and carried on a common hinge axis, theconvolutions are tilted away from the plane" surfaces and alsocircumferentially, the condition resulting from compressing the contactalong its toroidal axis. Thus, the multiple convolutions are eachindependent of the others and each convolution in turn vdefines'vparallel independent paths for current to flow between points ofcontact. There is an adequate mass of metal surrounding the interchangepoints for accepting current and any Fig. 1 is a side elevational viewof an air disconnect switch embodying the invention;

Fig. 2 is an enlarged fragmentary top view of the blade actuatingmechanism at the hinge end of the switch in Fig. l;

Fig. 3 is a fragmentary sectional View of the bearing assembly and thenovel means for transferring current between concentric members such asfrom the switch blade to its guide housing;

Fig. 4 is a fragmentary sectional view taken on a line correspondingwith 4-4 of Fig. 3, looking in the direction of the arrows;

Fig. 5 is a fragmentary enlarged sectional view of the novel means fortransferring current between parallel, relatively rotatable members suchas in the transverse hinge joint of the switch depicted in Fig. 2;

Fig. 6 shows a portion of a current interchange contact confined betweenconcentric cylinders and another portion confined between parallelplates, one purpose of the diagram being to illustrate the meaning ofthe terms inside and outside diameter as used in the designcalculations;

Fig. 7 shows one enlarged convolution of the interchange contact removedfrom a concentric cylinder application, Fig. 4 for example, one of thepurposes of the view is to identify symbols used in the designcalculations;

Fig. 8 shows one convolution of the interchange contactremoved from aplane or parallel plate application, Fig. 5 for example, whose purposeis to identify symbols used in the design calculations;

Fig. 9 is an end view of one convolution comparable to that exposedwhere a section is taken axially of the interchange contact as in Fig. 5and it is also comparable to a side elevation taken of Fig. 8 but withthe V-groove added; and,

Fig. l is a View of one convolution as depicted in either Figs. 7 and 8looking along a line normal to the plane of the respective convolutions.

The novel current interchange contact may be embodied in a Variety ofdevices such as circuit breakers and grounding switches but it is heredescribed in conjunction with a vertical break air disconnect switchillustrated in Fig. l. Without regard for improvements that constitutethe instant invention, the switch is generally comparable to one shownand claimed in the copending application of T. A. Fjellstedt, f iledAugust 1l, 1954, Serial No. 449,129, and assigned to the assignee ofthis application, so details are available from that source. For presentpurposes. however, it is suflicient to say that the switch ischaracterized by a channel iron mounting base 1 upon which stands frontand rear stationary insulators Z and 3, respectively. Operation of theswitch is accomplished bv axially rotating an intermediate insulator 4through swinging an operating lever that is bolted to a suitable flangering attached to a post 6 that carries the insulator 4. The lower end ofthe insulator 4 assembly is journalled in a bearing structure 7 and theupper end is journalled at 8 in the bottom of a stationary support frame9. When lever 5 is swung it causes, by means of mechanism to bedescribed. the main switch blade 10 to rotate longitudinally and riseangularly to a full open position.

The switch actuating mechanism includes a crank 14 fixedly held to thetop of rotating insulator 4 by cap screws, for example. When crank 14swings, a torque is transmitted to blade 10 by means of a link 15 whichis connected to one end of crank 14 by a ball joint 16. The other end oflink 15 engages blade 10 through the agency of a blade carriage 17 thatis secured tightly on the blade by means of a cap screw 18. Carriage 17is tubular for permitting blade 10 to extend through it and it also hasa cylindrical extension portion 19, see Fig. 3, that enables it to bejournalled in a concentric blade guide member 20 in ball bearings 21held by a retainer ring 22 in a manner clearly evident in the last namedfigure. Thus, it is seen 4 that blade 10 is journalled for low frictionrotation on its longitudinal axis within blade guide 20.

Cylindrical blade guide 20 has a pair of blade pivot arms 23 integrallycast with the former. Pivot arms 23 are adapted to swing on an axistransverse to the axis of blade 10 so that the blade will rise anddescend angularly as well as rotate longitudinally when insulator 4 isturned. The axis for swinging the blade is coincident with that ofopposite hexagon head bolts 24 which serve as shafts and means forphysically holding opposite guide arms 23 between sides of fixed supportcasting 9, see Figs. 2 and 5 in particular.

Blade 10 is generally an extruded tubular shape but it has a flattened,beaver tail end 28 where it is engaged between sides of a stationaryhigh pressure contact assernbly 29 or any other suitable contact.Stationary contact 29 is conductively supported on a terminal casting 30to which an incoming line wire, not shown, may be attached.

At the rear end of the switch, support frame 9 is secured to the top ofstationary insulator 3 in the vicinity of where reference numeral 31 isapplied. The remote rear end of casting 9 is so configured, see Fig. l,that it cooperates with a bolted pressure pad 32 for compressivelyengaging an outgoing line wire 33 as shown.

From the structure described thus far it will be evident that when theswitch of Fig. 1 is closed and conducting, current is exchanged from jaw29, to blade 10, through an axial joint to blade guide 20, through ahinge joint to casting 9 and to the outgoing line 33. The presentinvention is primarily concerned with improving the efficiency of thecurrent interchanges from blade 10 to guide 20 and from blade guide arms23 to casting 9 and the description now proceeds with a more detaileddiscussion of the novel aspects for achieving improvement in this area.

Transfer of current between concentric elements such as blade 10 andguide 20 will first be described primarily in reference to Figs. 3 and 4which are portions of the Fig. l switch isolated for enlargement andfacilitating description.

A portion 36 of blade 10 is diametrically enlarged so that a copper orthe like interchange contact retainer collar 37 may be easily slid overthe blade and pressfit or brazed on the enlarged portion 36. Theelectrical resistance between collar 37 and blade 10 is immeasurablysmall so that this particular joint is not treated as an interchange atall. The external periphery of collar 37 defines an annular channel thatis V-shaped in cross section for the purpose of retaining and providinga seal for the multiple point current interchange spring-like contact38. The surfaces 39 and 40 that define the bottom of the V-groovediverge from each other at an included angle of about ninety-degrees inthis example, although a different angle is also acceptable practice.However, it will be noted that the side 40 projects at an angle axiallyof the blade 10 and extends beyond the ends of guide cylinder 20 fordefining a triangular seat in which is disposed an elastic sealing ring41, preferably of silicone nlbber. This sealing arrangement excludescontaminants from the interior of guide cylinder 20 and permits packingthe region about contact 38 and the ball bearings 2?.. with corrosioninhibiting, constant viscosity lubricant such as a silicone base grease.

Attention is now focused on the general character of the novel element38 which interchanges current from collar 37 to the guide cylinder 20when blade 1i) is static or during rotation on its longitudinal axis.Details for designing such a spring-like current interchange contactwill be discussed more fully later in a manner applicable to theembodiment of Fig. 5 as well as Fig. 3 and then further as specificallyapplicable to those respective tigures. For the present it may be notedthat interchange contact 38 is comparable to a helical spring that isdisposed about the V-groove of collar 37 with the convolutions tilted ina circumferential direction of the toroid thus defined. The contact 33is originally wound on a mandrel, like a continuous run of ordinaryhelical spring, but a portion including a definite number of individualturns or convolutions is then cut olf and the free ends joined by anysuitable means that causes the Various turns to lie close to each other'at the junction so that no gap appears which might reduce the number ofeffective contact points. The number of individual convolutions in eachinterchange contact 38 is determined in a manner mentioned later, but itmay be noted in Fig. 4 that they lie quite closely against each other.

Note particularly in Fig. 3 that the contact 38 has a multiplicity ofbearing points resulting from each convolution touching the sides 39 and40 in tangency Where the lead lines of those numerals are affixed andthat there is an opposite contact point 43 diametrically opposite theapex of the V-groove. Thus, each turn constitutes a pair of parallelcurrent paths between points 43 and 40, and points 43 and 39. TheV-groove has great signiicance in that it creates the paths andfurthermore shortens them, thereby reducing the resistance drop ofinterchange contact 38.

Other important advantages are afforded by this construction. Forexample, static seizure or peak frictional drag between the contact jawand blade is virtually eliminated by reason of a multiplicity ofrelatively low pressure current interchange points being always incontact and uniformly distributed about the axis of rotation of theparts. This contrasts with prior art so-called high pressure contactsusually involving two to six points of interchange that bear in veryintense frictional engagement which must be overcome during the initialstage of switch opening and the nal stage of switch closing.

Moreover, the distributed, relatively low pressure contacts of theinstant invention reduced wear on any particular point. Therefore thelikelihood of switch failure is not as great as where yonly va smallnumber of interchange points are used and all reliance is placed on thelatter. Because the novel interchange contact lends itself readily tosealing and permanent lubrication, contact deterioration and periodicmaintenance are both reduced to insignicance.

The novel interchange contact mitigates other disadvantages inherent inswitches employing pairs of high pressure interchange contacts such asof the butt or wiping types that effectively interchange between onlytwo, or at best, a very limited number `of points. prior art contacts,when current is forced to converge from a broad conductive mass to ahigh density interchange point and then broaden out again, severaleifects are produced that contribute to thermal failure. Among them isthe phenomena of eonstrictive resistance and change of materialresistivity with temperature which is characterized by a marked increasein effective resistance at points of high current concentration. Anincident to this phenomena is that by converging the current to a point,the eiective heat absorbing mass and heat dissipating area lare reduced,while the heat generated by current flow is increased. The thermalcondition in prior art high pressure contacts is further aggravated bythe fact the heat energy produced is a function of the current squared.With the heavy fault currents that these contacts are called upon 4towithstand, the generated heat energy can easily reach an unsafe level.These thermal effects are overcome in the instant invention by replacingthe two, or at best, a limited number of interchange points with manyseparate paths `dispersed over a nomirrally broad area. The generationof heat energy is now a function of the sum tof the squares of smallvalues of current in each individual multiple path. A non-linearreduction introduced by the square of the current accounts for anenormous reduction in heating effect and at the same time the currentand heat yare distributed over a greater mass and dissipating area.

InV these YDisposing thespring-like currentv interchange contact in theV-groove, described earlier in connection with one embodiment, has theadvantage of shortening the current paths through the individualconvolutions and aids in rapid conduction of heat therefrom.

Magnetic considerations are also important. In a point contactinterchange where the current constricts for passing through a smallarea, electromagnetic repulsive forces are produced which tend toseparate contact members and reduce their mutual contact pressure whenit is most urgently needed. This force is also a function of the currentsquared, so dividing the current ow into a multiplicity of separatepaths deployed in a radial pattern Y reduces these forces toinsignilcance.

Attention is nowV turned to the embodiment where a current interchangecontact, designated 48 to distinguish it from the contact 38 in Figs. 3and 4, is disposed between relatively rotatable parallel members such asin the blade guide hinge joint of Fig. 2 and its enlargement in Fig. 5.In this case the contact 48 has its convolu-l tions tilted in a planenormal to the toroid axis resulting from compressing the contact endwisealong the axis of hinge pivot bolt 24. Switch hinge arms 23 terminate inan integrally cast pad 49 that is provided on its complementary planarface S0 with an annular interchange spring contact retaining V-groovedeiined by diverging bottom surfaces 51 and 52 and an interior axialwall 53. 'Ihe convolutions of contact 48 are tangent to surfaces 51 and52 where touched by the lead lines of those' numerals and the face 46 ofcasting 9 is contacted by the convolutions at 54, thus creating acircular point contact pattern and parallel paths in each convolutionwith advantages enunciated earlier.

It will appear later where the design data is set forth, that the termparallel surfaces means a pair of planes taken transverse to the axis ofrotation of two parts. ln Fig. 5 this would be a plane such as 46 takenin con junction with an imaginary parallel plane Vthat includes a pointdiametrically opposite on a convolution from the point of tangency 54.This is further exemplified in Figs. 8 and 9. In other words, design ofthe contact at rst disregards the presence of the V-groove. Y p

The surfaces 51 and 52, constituting the V-groove bottom, diverge fromeach other at an angle of approximately one hundred and twenty degreesin this Vinstance and it will be noted in Fig. 5 that 52 is longer than51. Moreover, groove wall 53 is of such length that it creates a centralhub which allows placement and retention of the toroidal spring so thatassembly is made easier. This is possible since the toroid in itsnatural condition tends to contract to form the smallest circle when notcompressed axially into the bottom of the groove. When, during assembly,hinge arms 23 are placed between sides of casting '9,Y the toroiddiameter increases and the contact 48 spreads until it bears on points51, 52 and 54. This also imparts the proper inclination to theindividual convolutions.

Note that hinge bolt 24 has a truncated conicular portion 5S at its headend that enables placement of an elastic circular sealing ring 56 inself tightening condition. Hinge bolt 24 is screwed into casting 9 buthas a smooth bearing surface where it passes through pad 49 of hinge arm23 and a jam nut on the bolt sets it when compression of the spring hasbeen adjusted nally. The V-groove of the hinge bearing assembly is alsopacked, for life time lubrication of the current interchange =48 and thebolt shaft, with corrosion inhibiting constant viscosity lubricant suchas silicone grease. Con-` taminants are excluded and the grease isretained by a flexible seal ring 59 residing on an annular bevel as is'Aclearlyevident in Fig. 5. p.

The current interchange spring-like contacts 38'anld 48 are preferablymade fromahigh conductivity, high temperature resistant spi'rm'gmaterial.` It has been found that among currently available material,Beryllium copper alloy No. 10 has the best conductivity, physicalproperties, and the ability to withstand any expected thermal effectwithout change of properties.

In the ensuing paragraphs procedure for designing a current interchangespring contact will be set forth. As stated earlier and according to theimplication of the disclosure there are two general cases which must beconsidered. One is where the contact is used between concentric,generally cylindrical elements as represented most clearly in Figs. 3,4, 6 and 7, and two, where the contact is used between nominallyparallel planes that are hinged together as most clearly shown in Figs.5, 8 and 9.

The design procedure is based on calculating a springlike contact havingmaximum current carrying capacity for a given space. Error on the sideof a greater safety factor is inherent in the procedure where physicalconfiguration, such as a minimum shaft size, becomes controlling. Inaddition, recommendations are made for the practical range of many ofthe constants employed that have been verified by experience.

I. Spring interchange Contact cross sectional area The total effectivecross sectional conducting area of spring material required in aparticular design will depend upon the current carrying requirements ofthe switch and the allowable Vcurrent densities. This applies in aconcentric `cylinder or a parallel plate application. The currentdensity is governed by experience and should be verified by thegenerally acceptable switch testing practices since it is difficult topredict the steady state heat dissipation characteristics of a designbased on purely theoretical considerations. With a spring contactmaterial having a conductivity of above 50% (International AnnealedCopper Standard) it is feasible to use densities in the range of 1000 to2000 amperes per square inch.

In a design having large current carrying requirements it is usuallypreferable to use more than one spring contact in parallel, that is,arranged axially or concentrically of each other to reduce the currentload on each spring contact.

Let:

Ai=total cross sectional conducting area required, in

square inches.

1=steady state load current in amperes.

Fzsteady state current density in amperes per square inch.

Then:

A- I h --F square mc es II. Approximation of wire diameter This alsoapplies to the concentric cylinder and parallel plate cases. To simplifythe design procedure an approximation can be made for the wire diameterbased upon area, angle of layover (tp in Figs. 7 and 8) and apre-selected final inside diameter (DI in either case shown in Fig. 6).The approximate final inside diameter of the spring contact whenconfined must be selected in view of space considerations of theproposed interchange assembly. In other words, the inside diameter maybe governed to some extent by strength and size requirements of otherparts such as blade 10 or hinge bolt 24 and their associated elements.

Experience has shown that the angle of layover in either case should beapproximately 50 degrees for optimum design. The practical range of wirediameters has been found to run from B & S gauge No. 19 (.036 inch) to B& S gauge No. l (.102 inch). For the cases of Fig. 7 or 8, wire sizeconsiderations are the same.

Let: d^=approximate wire diameter in inches. DI'==approXimate finalinside diameter of spring toroids 38 and 48 in inches.

8 =angle of layover in Figs. 7 and 8 (50 degrees recommended). Then:

d illCllGS If wire size falls outside of range suggested above, go backand reduce current density F or area per spring contact A, adopt twosprings if necessary to meet this requirement. After the approximatewire size has been found, in the usual case, select the nearest standardwire size. From this the number of turns or convolutions in eachspringcontact can be calculated from:

2A N an Where N=number of turns per spring contact. dzwire diameter ininches.

III. Short circuit temperature rise ICt-i- To degrees F.

Where T=rnaximum short circuit temperature in F.

T0=initial temperature prior to short circuit (ambient plus steady staterise).

Ic=short circuit current per spring path.

I =total short circuit I r=time duration of short circuit in seconds.

amparos per current path *i Cls p=resistivity of the spring contactmaterial in ohms per square inch per inch =density of spring contactmaterial in pounds per cubic inch s=specific heat of spring contactmaterial in B.t.u. per

pound per degree F.

'v t e4 ohmj inches o E btu.

After calculating the theoretical maximum temperature rise T, acomparison must be made with the permitted rise for the equipment beingdesigned. Knowing the temperature withstand properties of the springcontact material particularly, a determination must be made as towhether the contact will successfully pass a heat run after shortcircuit conditions have subsided. Bear in mind that the calculatedtheoretical rise is based on the worse conditions. If this `temperaturerise is less than that allowable for the material, it may be assumedthat the large masses of metal confining the spring contact will carryaway and radiate heat so that the theoretical rise will never bereached. This introduces a large safety factor into the design at thispoint.

C1 is expressed in IV. Calculations for parallel surface application Thepreceding computations apply to both cases. Special consideration willnow be given to application of the spring Contact between two adjacentparallel surfaces amarsi" for' interchanging current between them as inthe hingeV wp=turn space factor for parallel surface applications,

see Fig. 8.

DI=nal inside diameter of spring contact in inches,

see Fig. 6.

D=mean diameter of single turn in inches, see Fig. 10. (Fig. l is a viewlooking at a right angle to the long side of either of the turns inFigs. 7 or 8, recognizing that one portion a turn lies over the otherand causes an appearance of foreshortening.)

C2=spring contact ratio factor, explained below.

f=spring contact turn deilection in inches, during layover.

G=gap between parallel planes against which actual contact by the springis made, see Fig. 8.

(1) wp= COS qs inches (2) D1=V% d inches When a definite inside diameterDI has been set by other design limitations, the number of turns N canbe varied slightly.

(3) D=C2d inches If the maximum temperature under short circuitconditions T is high compared to the allowable maximum for the springcontact material, it is benecial to hold C2 as low as possible so thatheat may be conducted away from the critical mid-turn zone of the springcontact. For lower values of C2, that is, for stiller spring contacts,it has been found that some permanent set will result but Withoutdetrimental effect on performance.

Larger values of the ratio factor C2 will yield Va softer spring contacthaving less contact pressure and therefore less frictional drag. In someapplications it is desirable to avoid permanet set and this requires amore detailed examination of the spring wire fiber stresses. Thiscomputation will be set forth under item 6 below.

This is an approximate value of spring deection f that is accurateenough for normal applications.

)0:3022 sin 4S inches In the range of 8.5 to 13 for the spring ratiofactor C2, the maximum tensile liber stress occurs in the expandedhalf-turn.

feEK., -lpounds per square inch V. Calculation for concentric cylinderapplication In this application a current interchange contact spring 38is disposed between concentric cylinders particularly illustrated inFigs. 3, 4, at 38 in Fig. 6, and in Figs. 7 and l0. Here it is necessaryto determine the cylinder diameters and the spring contact dimensions.The V- groove does not enter into the computations until later and atimely showing will be made concerning'how to calculate the grooveangle. DI and D0 are not affected by the presence of the V-groove.

Let:

(l) Y 106:2@ inches c s qS N (2) Dr: Arwcd inches When a deiinite DI hasbeen set by design limitations, .th number of turns may be variedslightly.

(3) D=C2ol inches Select C2 as set forth under part IV, item 3.

(4) f sin inches See comment in part IV, item 4. The same considerationsare here involved.

(6) Follow same procedure as in part IV, item 6 where the stresscalculations are set forth.

VI. Calculation of V-groove dimensions for either concentric cylinder orparallel plane applications Approximate formulas, suflicient-ly accuratefor practical purposes are given below for calculating the V- groovedimensions to be used with current transfer spring contacts. The symbolsused are identical to those defined earlier except Athat certain symbolsappearing only in Fig. 9 are now to be introduced. In order toappreciate the ensuing calculations as they apply to a parallel plateapplication, those versed in the art will be interested in knowing thatby theory and inspection it has been discovered that the outsidediameter of a spring convolution does not change when the individualconvolutions are tilted during connement. This allows treating aconvolution as it appears in Fig. 9, for example, as a true ellipse andfacilitates computing the points where the V-groove is tangent to theperiphery lof each convolution.

The V-groove angle 0 is preselected in view of theV ll geometry of thewhole interchange design and machining convenience. In Fig. 3 forinstance, the angle is such that the seal ring 41 can be located withinreasonable dimensional limits of collar 37. Experience dictates that 30to 45 degrees is a satisfactory angle 0.

All preceding calculations for designing an interchange spring contactare based upon use of smooth concentric cylinders or smooth planesurfaces that are tangent to each turn only at diametrically oppositepoints. Addition of the V-groove does not invalidate any of thosecalculations. The groove serves as a means for restraining the springcontact in predictable alignment and it further creates two currentpaths in each turn accompanied by advantages set forth earlier.

Attention is now invited to Fig. 9.

The calculation of (z) yields a dimension that may be added to the gapdimension (G) for parallel plate applications, see Fig. 8, or subtractedfrom DI for a concentric cylinder application, see Fig. 7, forestablishing the apex of the V-g-roove. Machining is easier if the apexis given a slight radius or illet and skilled designers can readilyunderstand how to do this.

Although this invention has been described in considerable detail inreference to an air disconnect switch, it is to be understood that suchdescription is intended as illustrative rather than limiting, for theinvention may be variously embodied in other electrical apparatus suchas circuit breakers and oil switches. Therefore the invention is to beinterpreted in View of the claims which follow.

It is claimed:

l. An air disconnect switch comprising a stationary terminal, blademeans adapted to rotate on its longitudinal axis for cooperatingelectrically with said terminal, blade guide means including acylindrical portion surrounding a portion of said blade means inconcentric spaced relation to define an annular gap, at least one ofsaid portions being provided with an annular groove dened by divergingsides that are presented toward said other portion, contact meansdisposed in said gap for eiecting sliding electrical connection betweensaid blade and guide means, said contact means comprising a toroidallyshaped helical Spring-like member including a multiplicity of turnswhich have spaced points on their peripheries tangent to the divergingsides of said groove and at least another point tangent to the lother ofsaid portions whereby short parallel current paths are created in eachturn bridging said gap, the individual turns having their planesinclined at an angle with respect to a plane passing axially throughsaid blade means, whereby the inherent resiliency of said turnsmaintains them in firm frictional relation between said portions.

2. An air disconnect switch comprising a stationary terminal, blademeans adapted to swing on a transverse axis for cooperating electricallywith said terminal, pivot shaft means on which said blade means swings,a stationary support for said shaft means, said blade means and saidstationary support each having nominally planar portions incomplementary adjacence and adapted for relative rotation about saidpivot shaft means, at least one of said planar portions being providedwith an annular groove surrounding the pivot axis and having divergingsides presented in the direction of the pivot axis, contact meansdisposed circumferentially around said groove for interchanging currentbetween said planar portions, said contact means comprising a toroidallyshaped helical spring-like member including a multiplicity of turnswhich have spaced pointson their peripheries tangent to the divergingsides of said groove and at least another point tangent to the other ofsaid portions whereby short parallel current paths are created in eachturn bridging said planar portions, the individual turns having theirplanes inclined at an angle with respect to a plane normal to said pivotaxis, whereby the inherent resiliency of said turns maintains them iniirm frictional relation with said parallel portions.

3. An air disconnect switch comprising a stationary terminal, blademeans adapted to rotate on its longitudinal axis for cooperatingelectrically with said terminal, said blade means being provided nearone end with an annular groove defined by diverging sides that arepresented radially outward, blade guide means including a cylindricalportion surrounding said groove in concentric spaced relation to dene anannular gap, contact means disposed in said gap for effecting slidingelectrical connection between said blade and guide means, said contactmeans comprising a toroidally shaped helical spring-like memberincluding a multiplicity of turns which have spaced points on theirperipheries tangent to the interior of said cylindrical portion andother points tangent to the diverging sides of said groove wherebyparallel current paths are created in each turn between said blade meansand cylindrical portion, the individual turns having their planesinclined at an angle with reference to a plane passing axially throughsaid blade means, whereby the inherent resiliency of said turnsmaintains them in lrm frictional relation between said diverging sidesand said cylindrical portion.

4. An air disconnect switch comprising a stationary terminal, blademeans adapted to rotate on its longitudinal axis for cooperatingelectrically with said terminal, said blade means being provided nearone end with an annular groove having diverging sides projectingradially outwardly from the blade, a housing including a cylindricalportion surrounding a part of said groove in concentric spaced relationto deline an annular gap, at least one of said `diverging sidesprojecting axially beyond said housing and in proximity therewith todefine an angular seal seat, a circular elastic sealing ring bearinginto the angle of said seat and thereby sealing the region of thegroove, and contact means disposed in said groove` for eiecting slidingelectrical connection between said blade means and housing, said contactmeans comprising a toroidally shaped helical spring-like memberincluding a multiplicity of turns whose planes are inclined at an anglewith respect to a plane passing axially through said blade means.

5. =In electric apparatus including conductive elements that are hingedfor relative rotation about a common axis, the combination of a rstelement and a second nominally parallel element adjacent thereto alongthe axis of rotation to dene a gap therebetween, at least one of saidelements being provided with a groove encompassing the axis of rotationand which groove in cross section is characterized by radially divergingsides presented toward the other of said elements, contact meansdisposed in said gap for interchanging current between said elements,said contact means comprising a toroidally shaped helical spring-likemember including a multiplicity of turns which have spaced points ontheir peripheries tangent to the diverging sides of said groove and atleast another point tangent to the opposite element whereby shortparallel current paths are created in each turn, the individual turnshaving their planes inclined at an angle with respect to a plane normalto the rotational axis, whereby the inherent resiliency of said turnsmaintains them in tirm frictional relation with said elements.

6. In elec-tric apparatus including conductive elements that arerotatable relative to each other, the combination of a cylindricalinternal element and a cylindrical eX- ternal element surrounding a partof the rst named element in concentric spaced relation to deiine anannular gap therebetween, at least one of said elements being providedwith an annular groove in the region of said gap whose cross section ischaracterized by radially diverging sides presented toward the other ofsaid elements, contact means in said gap comprising a toroidally shapedhelical spring-like member including a multiplicity of turns which havespaced points on their peripheries tangent to said diverging sides andat least another point tangent to the other of said concentric elementswhereby parallel current paths are created in each turn bridging saidgap, individual turns having their planes inclined at an angle withrespect to a plane passing axially through the cylindrical elements,whereby the inherent resiliency of said turns maintains them in irmfrictional relation between the elements.

7. In electric apparatus including conductive elements that are movablerelative to each other, the combination of a substantially cylindricalinternal element and a substantially cylindrical external elementsurrounding a part of the first named element in concentric 4spacedrelation to dene an annular gap therebetween, at least one of saidelements being provided with an annular groove in the region of said gapwhose cross section is characterized by diverging sides presented towardthe other of said elements, contact means in said gap comprising atoroidally shaped helical spring-like member including a multiplicity ofturns which have spaced points on' their peripheries tangent to saiddiverging sides and at least another point tangent to the other of saidconcentric elements whereby parallel current paths are created in eachturn bridging said gap, individual turns having their planes inclined atan angle with respect to a plane passing axially through the cylindricalelements, 'whereby the inherent resiliency of said turns maintains themin firm frictional relation between the elements.

References Cited in the tile of this patent UNITED STATES PATENTS2,436,296 Graybill et al. Febr. 17, 1948 2,449,479 Hopper et al. Sept.14, 1948 2,734,955 Owens Feb. 14, 1956 FOREIGN PATENTS 186,526 GreatBritain Oct. 5, 1922

